Image forming apparatus and recording material determination unit

ABSTRACT

An image forming apparatus includes an image forming unit for forming an image on a recording material, a first detection unit including a transmission unit for transmitting an ultrasonic wave and a reception unit for receiving the transmitted ultrasonic wave, first and second conveyance units for conveying the recording material, and a control unit. The first and second conveyance units form a loop on the recording material by conveying the recording material at different speeds. The control unit controls an image forming condition for forming an image on the recording material by the image forming unit, based on the ultrasonic wave received via the recording material in a period in which no loop is formed on the recording material by the first and second conveyance units.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for detecting grammage of arecording material with high accuracy.

2. Description of the Related Art

Some of conventional image forming apparatuses such as a copier and aprinter internally include a sensor for determining the type ofrecording material. These apparatuses automatically determine the typeof recording material and controls transfer and fixing conditionsaccording to the determination result. Examples of the transfercondition include a transfer voltage and a conveyance speed of therecording material during transfer. Examples of the fixing conditioninclude a fixing temperature and a conveyance speed of the recordingmaterial at fixing.

Japanese Patent Application Laid-Open No. 2009-29622 discusses an imageforming apparatus including an ultrasonic sensor that detects grammageof a recording material by transmitting an ultrasonic wave to therecording material and receiving the ultrasonic wave that has beenattenuated after being transmitted through the recording material. Theimage forming apparatus controls image forming conditions such astransfer and fixing conditions according to the grammage of therecording material that has been detected by the ultrasonic sensor. Forfeeding back the detection result to the transfer conditions, theultrasonic sensor is arranged on an upstream side, in a conveyancedirection, of a transfer unit that transfers an image onto the recordingmaterial.

Meanwhile, there has been a known control of forming a loop on arecording material when an image is transferred onto the recordingmaterial by the transfer unit. More specifically, a conveyance unit ispositioned on an upstream side of the transfer unit in the conveyancedirection of the recording material. The conveyance unit conveys therecording material to the transfer unit at a speed faster than that ofthe transfer unit, so that a loop is formed on the recording material bythe conveyance unit and the transfer unit. The reason for forming a loopon the recording material is that if the recording material is pulledfrom the conveyance unit while an image is being transferred onto therecording material by the transfer unit, the speed of the recordingmaterial may vary during the transfer to cause a problem in the imagebeing transferred. On the other hand, if a loop is formed on therecording material, a significant change may occur in the orientation ofthe recording material to affect a detection result of the ultrasonicsensor. If the image forming conditions are set based on an erroneousdetection result, image quality may be degraded.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, an image formingapparatus includes an image forming unit configured to form an image ona recording material, a first detection unit including a transmissionunit configured to transmit an ultrasonic wave and a reception unitconfigured to receive the transmitted ultrasonic wave, a firstconveyance unit arranged on an upstream side of the first detection unitin a conveyance direction of the recording material, and configured toconvey the recording material toward a position between the transmissionunit and the reception unit, a second conveyance unit arranged on adownstream side of the first detection unit in the conveyance direction,and configured to convey the recording material conveyed by the firstconveyance unit, wherein the first conveyance unit and the secondconveyance unit form a loop on the recording material by conveying therecording material at different speeds, and a control unit configured tocontrol an image forming condition for forming an image on the recordingmaterial by the image forming unit, based on the ultrasonic wavereceived via the recording material in a period in which no loop isformed on the recording material by the first conveyance unit and thesecond conveyance unit.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an image forming apparatusaccording to first to third exemplary embodiments.

FIG. 2 is a block diagram related to a grammage detection unit of arecording material determination unit according to the first to thirdexemplary embodiments.

FIGS. 3A and 3B are diagrams illustrating a conveyance position of arecording material according to the first to third exemplaryembodiments. FIG. 3C is a diagram illustrating a relationship between aconveyance position of the recording material and a detection resultobtained using an ultrasonic wave.

FIG. 4 is a timing chart according to the first exemplary embodiment.

FIG. 5 is a flowchart according to the first exemplary embodiment.

FIG. 6 is a block diagram related to a surface property detection unitaccording to the second and third exemplary embodiments.

FIG. 7 is a diagram illustrating an arrangement relationship between thegrammage detection unit and the surface property detection unitaccording to the second exemplary embodiment.

FIG. 8 is a timing chart according to the second exemplary embodiment.

FIG. 9 is a flowchart according to the second exemplary embodiment.

FIG. 10 is a diagram illustrating a relationship between a conveyancespeed of a recording material and a detection result obtained using anultrasonic wave according to the third exemplary embodiment.

FIG. 11 is a timing chart according to the third exemplary embodiment.

FIG. 12 is a flowchart according to the third exemplary embodiment.

FIGS. 13A and 13B are block diagrams of a recording materialdetermination unit according to other exemplary embodiments.

FIG. 14 is a configuration diagram of an image forming apparatusaccording to a fourth exemplary embodiment.

FIGS. 15A to 15D are diagrams for describing erroneous determination dueto bending in the recording material.

FIG. 16 is a diagram illustrating a control configuration of the imageforming apparatus according to the fourth exemplary embodiment.

FIG. 17 is a flowchart illustrating type determination processing of therecording material according to the fourth exemplary embodiment.

FIG. 18 is a configuration diagram of an image forming apparatusaccording to a fifth or sixth exemplary embodiment.

FIG. 19 is a diagram illustrating a control configuration of the imageforming apparatus according to the fifth exemplary embodiment.

FIG. 20 is a flowchart illustrating type determination processing of therecording material according to the fifth exemplary embodiment.

FIG. 21 is a diagram illustrating a control configuration of the imageforming apparatus according to the sixth exemplary embodiment.

FIG. 22 is a flowchart illustrating type determination processing of therecording material according to the sixth exemplary embodiment.

FIGS. 23A to 23C are diagrams illustrating positional relationshipsbetween a grammage detection sensor and a guide roller of the imageforming apparatus, and the recording material according to the fourthexemplary embodiment.

FIGS. 24A to 24C are diagrams illustrating positional relationshipsbetween a grammage detection sensor, a surface property detectionsensor, and a guide roller of the image forming apparatus, and therecording material according to the fifth or sixth exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, first to third exemplary embodiments of the presentinvention will be described with reference to the drawings. Theexemplary embodiments described below are examples and not intended tolimit the scope of the present invention.

An outline of an electrophotographic image forming apparatus to whichthe first exemplary embodiment is applicable will be described below.FIG. 1 is a schematic configuration diagram of an image formingapparatus 1 that employs an intermediate transfer belt 17 and has animage forming unit 50 for forming an image on a recording material P.

The image forming apparatus 1 is a tandem type color laser beam printerand configured to be able to output a color image by superimposing fourcolor toners as developers including yellow (Y), magenta (M), cyan C,and black (K). A cassette 2, as an example of a storage unit, stores therecording material P. The image forming apparatus 1 includes a supplyroller (sheet feeding roller) 4, a conveyance roller pair 5, and aregistration roller pair 6. The supply roller 4 supplies the recordingmaterial P from the cassette 2. The conveyance roller pair 5 conveys therecording material P supplied from the supply roller 4. A registrationsensor 34 is provided near the registration roller pair 6. Theregistration sensor 34 is an example of a monitoring unit that detectsfront and rear ends of the recording material P and monitors theposition of the front end of the recording material P.

Photosensitive drums 11 (11Y, 11M, 11C, and 11K) bear toners ofrespective colors. Charging rollers (charging units) 12 (12Y, 12M, 12C,and 12K) uniformly charge the respective photosensitive drums 11 to apredetermined potential. Laser scanners (exposure units) 13 (13Y, 13M,13C, and 13K) correspond to the respective colors. Process cartridges(development units) 14 (14Y, 14M, 14C, and 14K) visualize electrostaticlatent images formed on the respective photosensitive drums 11 by thescanners 13. Developing rollers 15 (15Y, 15M, 15C, and 15K) feed thetoner in the respective cartridges 14 to the respective photosensitivedrums 11. Primary transfer rollers 16 (16Y, 16M, 16C, and 16K) primarilytransfer the images formed on the respective photosensitive drums 11,onto the intermediate transfer belt 17. The intermediate transfer belt17 is driven by a driving roller 18 to rotate. A secondary transferroller 19 transfers the images formed on the intermediate transfer belt17, onto the recording material P. The rollers 18 and 19 form a nipportion. The images formed on the intermediate transfer belt 17 aretransferred onto the recording material P while the recording material Pis being nipped and conveyed at the nip portion. These are an example ofa transfer unit that secondarily transfers the images onto the recordingmaterial P. A fixing device 20 is an example of a fixing unit formelting and fixing the toner images secondarily transferred onto therecording material P, while conveying the recording material P. Theabove-described components from the photosensitive drums 11 to thefixing device 20 constitute an example of the image forming unit 50.

A discharge roller 21 discharges the recording material P, on which thetoner images have been fixed by the fixing device 20, to the outside ofthe image forming apparatus 1. The roller 4, the roller pairs 5 and 6,the rollers 18 and 19, the fixing device 20, and the roller 21 that arearranged along a conveyance path of the recording material P and a motor(not illustrated) for driving these components constitute an example ofa conveyance unit that conveys the recording material P. A recordingmaterial determination unit 30 determines the type of the conveyedrecording material P. The recording material determination unit 30 has agrammage detection unit 31 that detects grammage of the recordingmaterial P. The grammage detection unit 31 includes an ultrasonic wavetransmission unit 31 a and an ultrasonic wave reception unit 31 b. Therecording material determination unit 30 determines the type ofrecording material P according to the grammage detected by the grammagedetection unit 31. A control unit 10 includes a micro processing unit(MPU) (not illustrated) including a central processing unit (CPU) (notillustrated) or the like, and has a function of controlling the imageforming apparatus 1. The control unit 10 controls an electrophotographicprocess, and also serves as a determination unit that determines thetype of recording material P based on the information detected by therecording material determination unit 30. The control unit 10 determinesa print mode according to the determined type of recording material P,and controls various image forming conditions. Herein, examples of imageforming conditions include a conveyance speed of the recording materialP, a value of a voltage to be applied to the rollers 16 and 19, and atemperature at which the fixing device 20 fixes the images onto therecording material P. Furthermore, the control unit 10 may control, asan image forming condition, rotation speeds of the rollers 16 and 19 atwhich the images are transferred. Furthermore, the control unit 10 maycontrol, as an image forming condition, the rotation speed of a fixingroller of the fixing device 20 at which the images are fixed.

The recording material determination unit 30 that determines the type ofrecording material P according to the present exemplary embodiment willbe described in detail with reference to FIG. 2. FIG. 2 is a blockdiagram of the recording material determination unit 30 including thegrammage detection unit 31.

The grammage detection unit 31 in FIG. 2 includes the transmission unit31 a that transmits an ultrasonic wave and the reception unit 31 b thatreceives the ultrasonic wave. The transmission unit 31 a and thereception unit 31 b are arranged facing each other. When the recordingmaterial P is conveyed to a position between the transmission unit 31 aand the reception unit 31 b, the control unit 10 outputs a signal forstarting transmission of an ultrasonic wave, to a transmission controlunit 42. Herein, the position between the transmission unit 31 a and thereception unit 31 b (a detection position to be detected by the grammagedetection unit 31) is a position through which the ultrasonic wavetransmitted from the transmission unit 31 a passes. The transmissionunit 31 a transmits an ultrasonic wave of a specific frequency to therecording material P according to the control of the transmissioncontrol unit 42. The reception unit 31 b has a function of receiving theultrasonic wave transmitted through the recording material P (via therecording material P). A reception detection unit 43 outputs a peakvalue of a signal output according to the ultrasonic wave received bythe reception unit 31 b, to the control unit 10 as a received signal101. The control unit 10 detects grammage of the recording material Pbased on the received signal 101. When the detection result is obtained,the control unit 10 outputs to the transmission control unit 42 a signalfor stopping transmission of the ultrasonic wave. For example, when thedetected grammage of the recording material P is small, the control unit10 determines that the type of recording material P is thin paper. Whenthe detected grammage of the recording material P is large, the controlunit 10 determines that the type of recording material P is thick paper.

In the ultrasonic wave transmitted through the recording material P, apeak value in a waveform attenuates according to the grammage of therecording material P. For example, when the recording material P hassmall grammage (thin paper), the peak value of the ultrasonic wave islarge, and when the recording material P has large grammage (thickpaper), the peak value of the ultrasonic wave is small. If the controlunit 10 sets the fixing temperature of the fixing device 20appropriately according to the detected grammage, the following effectsare achieved. For example, for the recording material P with smallgrammage such as thin paper, setting the fixing temperature at lowtemperature decreases the required power. On the contrary, for therecording material P with large grammage such as thick paper, settingthe fixing temperature at high temperature or setting the conveyancespeed of the recording material P at slow speed improves the fixability.In this manner, the control unit 10 controls the image formingconditions of the image forming apparatus 1 based on the detectionresult of the grammage. In addition, the control unit 10 may directlycontrol the image forming conditions of the image forming apparatus 1based on the value of the signal 101, without detecting grammage of therecording material P.

Next, a period for which the grammage detection unit 31 detects therecording material P will be described. FIGS. 3A and 3B illustrateconveyance positions of the recording material P between the roller pair6 serving as a conveyance unit, and the roller 19 serving as a transferunit. As illustrated in FIG. 3A, a loop is not formed on the recordingmaterial P before the front end of the recording material P (the end onthe downstream side in the conveyance direction of the recordingmaterial P) reaches the roller 19 (nip portion between the rollers 18and 19). At this time, the recording material P is conveyed by theroller pair 6 and the recording material P is pressed against aconveyance guide 52, so that the conveyance position of the recordingmaterial P becomes stable. On the other hand, as illustrated in FIG. 3B,a loop is formed on the recording material P after the front end of therecording material P has reached the roller 19. When the recordingmaterial P is conveyed by both the roller pair 6 and the roller 19, ifthe recording material P is pulled by the roller 19 on the downstreamside, the speed of the recording material P may vary during transfer tocause deterioration in image quality. Accordingly, by making therotation speed of the roller pair 6 faster than the speed of the roller19, a loop is formed on the recording material P to suppress thepulling. The roller pair 6 and the roller 19, however, have a variationin product tolerance and abrasion due to a secular change, so that theroller diameter changes. Thus, the same loop is not always formed.Therefore, as illustrated in FIG. 3B, a large loop is formed in onecase, and a small loop is formed in another case.

FIG. 3C is a graph illustrating the relationship between the conveyanceposition of the recording material P and the signal 101 output by thereception detection unit 43. The value of the signal 101 is smaller in acase where the recording material P is conveyed to a position close to acentral position between the conveyance guides 51 and 52, as comparedwith a case where the recording material P is conveyed to a position (anend 61) near the conveyance guide 51 or a position (an end 62) near theguide 52. Accordingly, when the loop is formed within a conveyance path,the conveyance position of the recording material P varies, leading to avariation in the detection result of the grammage detection unit 31.

Considering the above, a desirable detection period of the grammagedetection unit 31 is a period in which the conveyance position of therecording material P is stable. That is, the period is a period in whichno loop is formed on the recording material P. The present exemplaryembodiment describes, as an example, a case where detection is performedin the period from a time point at which the front end of the recordingmaterial P has passed through a position between the transmission unit31 a and the reception unit 31 b, to a time point at which the front endof the recording material P reaches the roller 19. The period is notlimited to the above period as long as the conveyance position of therecording material P is stable and no loop is formed on the recordingmaterial P. For example, the period may be a period from a time point atwhich the rear end of the recording material P (end on the upstream sidein the conveyance direction of the recording material P) has passedthrough the roller pair 6 to a time point at which the rear end of therecording material P reaches the position between the transmission unit31 a and the reception unit 31 b. Even in this case, it is possible tocontrol the temperature at which the fixing device 20 fixes an imageonto the recording material P, and to control the rotation speed of thefixing roller of the fixing device 20. Accordingly, the period is aperiod in which the recording material P is conveyed by either one ofthe roller pair 6 and the roller 19 and is not conveyed by the otherone.

The detection period of the grammage detection unit 31 according to thepresent exemplary embodiment will be described with reference to atiming chart in FIG. 4. The timing chart in FIG. 4 illustrates theperiod from a time point at which the front end of the recordingmaterial P has passed through the registration sensor 34 to a time pointat which the front end reaches the fixing device 20. In the presentexemplary embodiment, the recording material P is conveyed at a constantspeed in this period. As described above, a desirable detection periodof the grammage detection unit 31 is the period in which the conveyanceposition of the recording material P is stable. This period correspondsto the period from the time point at which the front end of therecording material P has passed through the position between thetransmission unit 31 a and the reception unit 31 b, to the time point atwhich the front end of the recording material P reaches the roller 19.In the timing chart in FIG. 4, the period corresponds to a period fromtimings (a) to (b) in FIG. 4. Herein, the timing (a) in FIG. 4 indicatesa timing at which the front end of the recording material P has reachedthe position between the transmission unit 31 a and the reception unit31 b (detection position to be detected by the grammage detection unit31). The timing (b) in FIG. 4 indicates a timing at which the front endof the recording material P has reached the roller 19. A timing (c) inFIG. 4 indicates the timing at which the front end of the recordingmaterial P has reached the fixing device 20.

Next, a method for monitoring the front end position of the recordingmaterial P and a positional relationship in arrangement in a conveyancesystem will be described. In the present exemplary embodiment, the frontend position of the recording material P is monitored using the sensor34, a pulse motor (not illustrated), and the control unit 10. The numberof steps of the pulse motor has a proportional relationship with therotation distance. Therefore, the distance for which the recordingmaterial P has advanced after passing the roller pair 6 can be estimatedfrom the counted number of steps. The present exemplary embodimentassumes that 100 steps are required before the front end of therecording material P reaches the position between the transmission unit31 a and the reception unit 31 b and that 300 steps are required beforethe front end of the recording material P reaches the roller 19, withreference to the position where the front end of the recording materialP has passed through the roller pair 6. In addition, the presentexemplary embodiment assumes that 500 steps are required before thefront end of the recording material P reaches the fixing device 20.These numbers of steps described above are only examples. The number iscalculated by the control unit 10 based on diameters or the like of thepulse motor and the roller pair 6 that are to be used. In addition, themotor is not limited to the pulse motor. Herein, a method using thenumber of steps of the pulse motor has been described as a method formonitoring the position of the front end of the recording material P.However, the method is not limited to this. It is only required to beable to determine whether the front end of the recording material P hasreached a position between the transmission unit 31 a and the receptionunit 31 b. Therefore, it is also possible to perform management by time,in which measurement starts after a predetermined time has elapsed fromthe time point at which an output change has occurred in the sensor 34.Herein, detection by the grammage detection unit 31 is assumed to beperformed for 100 ms. The detection period is, however, not limited to100 ms because it is only required that the detection is completedbefore the front end of the recording material P reaches the roller 19.

A control sequence of the control unit 10 according to the presentexemplary embodiment will be described with reference to a flowchart inFIG. 5. Control based on the flowchart in FIG. 5 is executed by thecontrol unit 10 based on a program stored in a read-only memory (ROM)(not illustrated) or the like. After receiving a print instruction, instep S501, the control unit 10 first instructs supply of the recordingmaterial P from the cassette 2 and start of an image forming operation.According to the instruction, the recording material P is supplied bythe roller 4 from the cassette 2. Thereafter, the recording material Ppasses through the roller pairs 5 and 6, and an output of the sensor 34changes at a timing at which the front end of the recording material Ppasses through the roller pair 6. In step S502, it is determined whetherthe output of the sensor 34 has changed. If the output has changed (YESin step S502), then in step S503, the control unit 10 starts, from theoutput change timing, counting the number of steps of the pulse motor(not illustrated). In step S503, a timer count inside the control unit10 is also reset. In step S504, it is determined whether 100 steps havebeen counted from a timing (T=0) at which the output of the sensor 34has changed. If 100 steps have been counted (YES in step S504), thecontrol unit 10 determines that the front end of the recording materialP has reached the position between the transmission unit 31 a and thereception unit 31 b, and then in step S505, instructs start of adetection operation by the grammage detection unit 31. In step S506, itis determined whether the detection by the grammage detection unit 31has been performed for 100 ms. If the detection has been performed for100 ms (YES in step S506), then in step S507, the detection finishes. Instep S508, the control unit 10 determines the type of recording materialP based on a detection result obtained by the grammage detection unit31, and determines image forming conditions according to the determinedtype. The processing then finishes.

Furthermore, for obtaining more accurate detection results, the grammagedetection unit 31 does not perform detection after the front end of therecording material P has reached the roller 19, due to theabove-described reason. The description has been given of the case wherethe recording material P is supplied from the cassette 2. Alternatively,the recording material P may be supplied from an optional device (notillustrated) that is detachably attached the image forming apparatus 1.

According to the present exemplary embodiment, the above-describedconfiguration and operation can bring about the following effects.Performing detection in a period in which the conveyance position of therecording material P is stable can improve the detection accuracy ofgrammage of the recording material P. Furthermore, the improvement inthe detection accuracy of grammage of the recording material P enablesappropriate print mode setting, leading to enhanced quality of an imageto be formed.

In the present exemplary embodiment, there can be considered aconfiguration of separately providing, between the conveyance unit andthe transfer unit, a loop sensor for detecting an amount of loop of therecording material P. It is estimated that, if the amount of loop of therecording material P is maintained at a predetermined value using theloop sensor, and the detection by the grammage detection unit 31 isperformed in this state, theoretically, the same detection result isobtained as long as the recording material P has the same grammage. Thisconfiguration, however, requires an additional loop sensor, leading toan increase in costs. According to the present exemplary embodiment, thegrammage of the recording material P can be detected without adding aloop sensor, namely, without extra costs. The description herein is notintended to prohibit the addition of a loop sensor in the presentexemplary embodiment.

In a second exemplary embodiment, the description will be given of aconfiguration in which the recording material determination unit 30includes a surface property detection unit 32 that detects the surfaceproperty of the recording material P, in addition to the grammagedetection unit 31 that detects the grammage of the recording material P.Description on main parts is similar to that in the first exemplaryembodiment. Herein, therefore, only the parts different from the firstexemplary embodiment will be described.

Hereinafter, the recording material determination unit 30 thatdetermines the type of recording material P according to the presentexemplary embodiment will be described in detail. The recording materialdetermination unit 30 has the grammage detection unit 31 as illustratedin FIG. 2, similarly to the first exemplary embodiment. The recordingmaterial determination unit 30 further includes the surface propertydetection unit 32. FIG. 6 is a block diagram of the recording materialdetermination unit 30 including the surface property detection unit 32.

The surface property detection unit 32 illustrated in FIG. 6 includes anirradiation unit 32 a, a focusing unit 32 b, and an image capturing unit32 c. The irradiation unit 32 a irradiates a surface of the recordingmaterial P with light. The focusing unit 32 b forms an image ofreflected light emitted from the irradiation unit 32 a and reflected onthe surface of the recording material P (via the recording material P).The image capturing unit 32 c is a light receiving unit that receivesthe light that has been imaged by the focusing unit 32 b, and capturesthe received light as an image. When the recording material P isconveyed at a constant speed to a detection position to be detected bythe surface property detection unit 32, the control unit 10 outputs toan irradiation control unit 44 a signal for starting emission of light.Herein, the detection position to be detected by the surface propertydetection unit 32 is a position to which light can be emitted from theirradiation unit 32 a. The irradiation unit 32 a irradiates the surfaceof the recording material P with light according to control of theirradiation control unit 44. For adjusting a focal length to therecording material P, the recording material P is configured to bepressed, on a back surface thereof, by a component such as a conveyanceroller 70, so that the conveyance position is fixed. The roller 70 is anexample of a contact member that contacts the recording material Pirradiated with light, on a surface opposite to the surface irradiatedwith light. The roller 70 holds, from the back surface, a regionirradiated with light. The recording material P is conveyed in thedirection indicated by an arrow A in FIG. 6. The roller 70 rotates inthe direction indicated by an arrow B, along with the conveyance of therecording material P. The light emitted onto the recording material P iscaptured as an image by the image capturing unit 32 c via the focusingunit 32 b. In the present exemplary embodiment, a line sensor extendingin the width direction of the recording material P is used as the imagecapturing unit 32 c. By using a line sensor, an image can be capturedwhile the recording material P is being conveyed. The captured image isan image of the surface of the recording material P and is output to animage detection unit 45. The image detection unit 45 outputs a receivedsignal 102 to the control unit 10 according to image data. Herein, thereceived signal 102 can be, for example, information related to thesurface property, such as a difference between the maximum and minimumdensity values included in the image data. The control unit 10 detectsthe surface property of the recording material P based on the receivedsignal 102. After the detection result is obtained, the control unit 10outputs to the irradiation control unit 44 a signal for stoppingemission of light. When the detected surface of the recording material Pis rough, for example, the control unit 10 determines that the type ofrecording material P is rough paper. When the surface of the recordingmaterial P is smooth, the control unit 10 determines that the type ofrecording material P is coated paper.

The captured image varies according to the difference in the surfaceproperty (unevenness) of the recording material P. When the recordingmaterial P is rough paper having a rough surface, for example, anobtained image has a high percentage of shadow due to the emitted light.On the other hand, if the recording material P is coated paper having asmooth surface, an obtained image has less shadow. The recordingmaterial P such as coated paper having a smooth surface property has arelatively low resistance value and requires higher transfer current andhigher transfer voltage for transferring a toner image, as compared withthe case of the rough recording material P such as rough paper.Therefore, controlling by the control unit 10 the transfer current andtransfer voltage according to a detection result of the surface propertyis also effective for enhancing image quality. In this manner, thecontrol unit 10 controls the image forming conditions of the imageforming apparatus 1 based on the detection result of the surfaceproperty. In addition, the control unit 10 may directly control theimage forming conditions of the image forming apparatus 1 based on thevalue of the signal 102, without detecting the surface property of therecording material P.

Next, a period for which the surface property detection unit 32 detectsthe recording material P will be described. In the present exemplaryembodiment, as illustrated in FIG. 7, the detection units 31 and 32 arearranged side by side in a direction orthogonal to a conveyancedirection of the recording material P (width direction of the recordingmaterial P). In addition, since the recording material P is held by acomponent such as the roller 70 from the back surface as describedabove, the surface property detection unit 32 is not easily influencedby a loop. Meanwhile, for capturing a stable image by the line sensor(the image capturing unit 32 c), it is desirable that a conveyance speedof the recording material P to be imaged is constant. From the aboveaspects, a desirable detection period of the surface property detectionunit 32 is a period in which the conveyance speed of the recordingmaterial P is constant, regardless of presence or absence of a loop.

The detection period of the detection units 31 and 32 according to thepresent exemplary embodiment will be described with reference to atiming chart in FIG. 8. The timing chart in FIG. 8 illustrates a periodfrom a time point at which the front end of the recording material P haspassed through the registration sensor 34, to a time point at which thefront end reaches the fixing device 20. In the present exemplaryembodiment, the recording material P is conveyed at a constant speed inthis period. A desirable detection period of the grammage detection unit31 is a period similar to that in the first exemplary embodiment. Thedetection period of the surface property detection unit 32 is notparticularly specified because the conveyance speed of the recordingmaterial P is constant. Thus, the period is only required to be a periodin which the recording material P exists at the detection position to bedetected by the surface property detection unit 32. In FIG. 8, theposition between the transmission unit 31 a and the reception unit 31 b(detection position to be detected by the grammage detection unit 31),and the detection position to be detected by the surface propertydetection unit 32 are assumed to be at substantially the same positionin the conveying direction of the recording material P. Therefore, thedetection period of the surface property detection unit 32 is set to aperiod from timings (a) to (c) in FIG. 8. Herein, the timings (a), (b),and (d) in FIG. 8 indicate the same timings as the timings (a), (b), and(c) in FIG. 4, respectively. Herein, the timing (c) in FIG. 8 indicatesa timing at which the rear end of the recording material P has reachedthe position between the transmission unit 31 a and the reception unit31 b (detection position to be detected by the grammage detection unit31). The period from the timings (a) to (c) in FIG. 8 includes a periodin which a loop is formed on the recording material P. In this manner,the conveyance speed of the recording material P temporarily changesduring execution of loop control. The change, however, is as small astolerance and scarcely affects detection accuracy of the surfaceproperty detection unit 32. Therefore, in the present exemplaryembodiment, the recording material P can be considered to be conveyed ata constant speed during execution of the loop control.

Herein, detection by the grammage detection unit 31 is assumed to beperformed for 100 ms. The detection period is, however, not limited to100 ms because it is only required that the detection finishes beforethe front end of the recording material P reaches the roller 19. Herein,detection by the surface property detection unit 32 is assumed to beperformed for 150 ms. In the present exemplary embodiment, the timetaken for the surface property detection unit 32 detecting the recordingmaterial P is secured as long time as possible in this manner, so thatmore image data can be obtained. As a result, the surface propertydetection accuracy by the surface property detection unit 32 isimproved. The detection period is not limited to 150 ms because it isonly required that the detection finishes before the rear end of therecording material P reaches the position between the transmission unit31 a and the reception unit 31 b. For example, for simplifying thecontrol, the detection by the surface property detection unit 32 may beperformed for 100 ms in harmony with the detection time of the grammagedetection unit 31.

A control sequence of the control unit 10 according to the presentexemplary embodiment will be described with reference to a flowchart inFIG. 9. Control based on the flowchart in FIG. 9 is executed by thecontrol unit 10 based on a program stored in a ROM (not illustrated).Control from steps S501 to S504 is performed similarly to the control inFIG. 5. In step S504, it is determined whether 100 steps have beencounted from the timing (T=0) at which the output of the sensor 34 haschanged. If 100 steps have been counted (YES in step S504), the controlunit 10 determines that the front end of the recording material P hasreached the position between the transmission unit 31 a and thereception unit 31 b, and then in step S601, instructs start of detectionoperations by the detection units 31 and 32. In step S602, it isdetermined whether the detection by the grammage detection unit 31 hasbeen performed for 100 ms. If the detection has been performed for 100ms (YES in step S602), then in step S603, the detection by the grammagedetection unit 31 finishes. In step S604, it is determined whether thedetection by the surface property detection unit 32 has been performedfor 150 ms. If the detection has been performed for 150 ms (YES in stepS604), then in step S605, the detection by the surface propertydetection unit 32 finishes. In step S606, the control unit 10 determinesthe type of recording material P based on the detection results obtainedby the detection units 31 and 32, and determines image formingconditions according to the determined type. The processing thenfinishes.

According to the present exemplary embodiment, the above-describedconfiguration and operation can bring about the following effects inaddition to the effects obtained by the first exemplary embodiment. Thatis, detecting not only the grammage but also the surface property of therecording material P enables more specific determination of the type ofrecording material P. Furthermore, holding the recording material P bythe conveyance roller can suppress the influence from the loop and makedetection time by the surface property detection unit 32 longer. Thisconsequently leads to improvement in the detection accuracy of thesurface property of the recording material P by the surface propertydetection unit 32.

In a third exemplary embodiment, the description will be given of thedetection periods of the detection units 31 and 32 that are set in acase where the conveyance speed of the recording material P is increasedor decreased. Descriptions on main parts are similar to that in thefirst or second exemplary embodiment. Herein, therefore, the partsdifferent from the first or second exemplary embodiment will bedescribed.

The conveyance speed of the recording material P is increased ordecreased for controlling the variation in a sheet interval (distancebetween the rear end of the preceding sheet and the front end of thesucceeding sheet) and for aligning a writing position where an image issecondarily transferred onto the recording material P. This brings abouteffects including improvement in throughput due to the shortened sheetinterval, and increased accuracy of an image forming position on therecording material P.

The relationship between the conveyance speed of the recording materialP and the detection result (received signal 101) obtained by thereception detection unit 43 using an ultrasonic wave will be describedwith reference to FIG. 10. Results (a), (b), and (c) in FIG. 10 indicatemeasurement results obtained when the roller pair 6 conveys therecording material P at a constant speed and before the front end of therecording material P reaches the roller 19. As seen from the results(a), (b), and (c) in FIG. 10, when the conveyance speed is not changed,there is no substantial difference between the detection results(received signals 101) obtained by the detection unit 43. Meanwhile,results (d) and (e) in FIG. 10 indicate measurement results obtainedwhen the roller pair 6 conveys the recording material P at an increasedor decreased speed and before the front end of the recording material Preaches the roller 19. The detection results are substantially equal tothe results (a), (b), and (c) in FIG. 10 described above. In thismanner, the conveyance position remains stable until the front end ofthe recording material P reaches the roller 19. Therefore, increasing ordecreasing the conveyance speed scarcely affects the detection result.From the above aspects, a desirable detection period of the grammagedetection unit 31 is, as described above, the period in which theconveyance position of the recording material P is stable, regardless ofincrease or decrease in the conveyance speed. On the other hand, adesirable detection period of the surface property detection unit 32 is,as described above, the period in which the conveyance speed of therecording material P is constant.

The detection periods of the grammage detection unit 31 and the surfaceproperty detection unit 32 according to the present exemplary embodimentwill be described with reference to a timing chart in FIG. 11. Thetiming chart in FIG. 11 illustrates a period from a time point at whichthe front end of the recording material P has passed through the sensor34, to a time point at which the front end reaches the fixing device 20.In the present exemplary embodiment, the recording material P isconveyed while the conveyance speed of the recording material P isincreased or decreased in a part of the period. A desirable detectionperiod of the grammage detection unit 31 is, as described above, theperiod in which the conveyance position of the recording material P isstable, regardless of increase or decrease in the conveyance speed. Thisperiod corresponds to the period from the time point at which the frontend of the recording material P has passed through the position betweenthe transmission unit 31 a and the reception unit 31 b, to the timepoint at which the front end of the recording material P reaches theroller 19. In the timing chart in FIG. 11, the period corresponds to aperiod from timings (a) to (c). Herein, the timings (a) and (c) in FIG.11 indicate the same timings as the timings (a) and (b) in FIG. 8,respectively. Accordingly, the detection period of the grammagedetection unit 31 is similar to that in the second exemplary embodimenteven when the conveyance speed is increased or decreased.

On the other hand, a desirable detection period of the surface propertydetection unit 32 is, as described above, a period in which therecording material P is conveyed at a constant speed. Therefore, in thetiming chart in FIG. 11, the period corresponds to a period from timings(b) to (d) in FIG. 11. Herein, the timing (b) in FIG. 11 indicates atiming at which the increasing/decreasing control of the speed of therecording material P has finished. The timing (d) in FIG. 11 indicatesthe same timing as the timing (c) in FIG. 8. In FIG. 11, similarly tothe second exemplary embodiment, the position between the transmissionunit 31 a and the reception unit 31 b (detection position to be detectedby the grammage detection unit 31) and the detection position to bedetected by the surface property detection unit 32 are assumed to be atsubstantially the same position in the conveyance direction of therecording material P. Based on this assumption, the detection period ofthe surface property detection unit 32 is defined. The present exemplaryembodiment has described the case where the length of the recordingmaterial P in the conveyance direction is shorter than the distancebetween the detection position detected by the surface propertydetection unit 32 and the fixing device 20. On the other hand, in a casewhere the recording material P longer in the conveyance direction thanthe distance is conveyed, the timing (the timing (e) in FIG. 11) atwhich the front end of the recording material P reaches the fixingdevice 20 comes earlier than the timing (the timing (d) in FIG. 11) atwhich the rear end of the recording material P reaches the detectionposition to be detected by the surface property detection unit 32. Inthis case, the detection period by the surface property detection unit32 is a period from the timings (b) to (e) in FIG. 11. That is, thedetection period corresponds to either one of the following periods thatis shorter than the other one: the period from the time point at whichthe increasing/decreasing control of the speed of the recording materialP has finished, to the time point at which the rear end of the recordingmaterial P reaches the detection position to be detected by the surfaceproperty detection unit 32, or the period from the time point at whichthe increasing/decreasing control of the speed of the recording materialP has finished, to the time point at which the front end of therecording material P reaches the fixing device 20. Herein, detection bythe surface property detection unit 32 is assumed to be performed for100 ms. The detection period, however, is not limited to 100 ms. It isonly required that the detection by the surface property detection unit32 finishes in a shorter period of the above-described periods, or in aperiod that is further shorter than the shorter period.

A control sequence by the control unit 10 according to the presentexemplary embodiment will be described with reference to a flowchart inFIG. 12. Control based on the flowchart in FIG. 12 is executed by thecontrol unit 10 based on a program stored in a ROM (not illustrated).Control from steps S501 to S507 is performed similarly to the control inFIG. 5. After step S507, it is determined in step S701 whether 300 stepsof the pulse motor have been counted. If 300 steps have been counted(YES in step S701), the control unit 10 determines that the front end ofthe recording material P has reached the roller 19, and then in stepS702, resets the timer. In step S703, the control unit 10 instructs thestart of the detection operation by the surface property detection unit32. In step S704, it is determined whether the detection has beenperformed for 100 ms. If the detection has been performed for 100 ms(YES in step S704), then in step S705, the detection by the surfaceproperty detection unit 32 finishes. In step S706, the control unit 10determines the type of recording material P based on the detectionresults obtained by the detection units 31 and 32, and determines imageforming conditions according to the determined type. The processing thenfinishes.

According to the present exemplary embodiment, the above-describedconfiguration and operation can bring about the following effects inaddition to the effects obtained by the first and second exemplaryembodiments. If the detection is performed in a period in which theconveyance position of the recording material P is stable, the detectionaccuracy of the grammage of the recording material P can be improvedeven when the conveyance speed of the recording material P is increasedor decreased. Furthermore, improvement in the detection accuracy ofgrammage of the recording material P enables appropriate print modesetting, leading to enhanced quality of an image to be formed.

Furthermore, in the present exemplary embodiment, the irradiation unit32 a may irradiate the recording material P with light in the period inwhich the conveyance speed of the recording material P is increased ordecreased. Note that, in this case, control is performed such that theresult obtained through image capturing by the image capturing unit 32 cis not reflected on the surface property detection result.Alternatively, the irradiation unit 32 a may be controlled not to emitlight in the period in which the conveyance speed of the recordingmaterial P is increased or decreased.

In the above-described exemplary embodiments, the transmission unit 31 amay transmit an ultrasonic wave to the recording material P in a periodin which the conveyance position of the recording material P is notstable. In this case, control is performed such that the result receivedby the reception unit 31 b is not reflected on the grammage detectionresult. Alternatively, the transmission unit 31 a may be controlled notto transmit the ultrasonic wave in the period in which the conveyanceposition of the recording material P is not stable.

In the above-described exemplary embodiments, the description has beengiven of the configuration in which the recording material determinationunit 30 is provided with the grammage detection unit 31 and the surfaceproperty detection unit 32. The configuration, however, is not limitedto this. The recording material determination unit 30 may be providedwith a detection unit that irradiates the recording material P withlight, receives the light transmitted through the recording material P,and detects the thickness of the recording material P based on theamount of the received light. Alternatively, the recording materialdetermination unit 30 may be provided with, instead of the surfaceproperty detection unit 32, a detection unit that irradiates therecording material P with light, receives the light reflected on therecording material P, and detects the surface property of the recordingmaterial P based on the amount of the received light.

The above-described exemplary embodiments have described a case where aloop is formed on the recording material P between the registrationroller pair 6 and the secondary transfer roller 19. The presentinvention is, however, not limited to this. For example, the presentinvention is also applicable to a configuration in which there are twoconveyance units that convey the recording material P and the grammagedetection unit 31 arranged therebetween, and a loop is formed betweenthe two conveyance units.

Furthermore, the above-described exemplary embodiments have describedthe recording material determination unit 30 configured to be fixed tothe image forming apparatus 1. The recording material determination unit30, however, may be configured to be detachably attached to the imageforming apparatus 1. When the recording material determination unit 30is configured to be detachable, for example, a user can easily replacethe recording material determination unit 30 when the unit 30malfunctions. Alternatively, the recording material determination unit30 may be simply configured to be additionally attachable to the imageforming apparatus 1.

Furthermore in the above-described exemplary embodiments, the recordingmaterial determination unit 30 and the control unit 10 may be integrallyformed and detachably attached to the image forming apparatus 1. Thisconfiguration is illustrated in FIGS. 13A and 13B. FIG. 13A is a blockdiagram of the recording material determination unit 30 including thegrammage detection unit 31. FIG. 13B is a block diagram of the recordingmaterial determination unit 30 including the surface property detectionunit 32. In this manner, if the recording material determination unit 30and the control unit 10 are integrally replaceable, when updating oradding a function of the recording material determination unit 30, auser can easily replace a sensor with the one having a new function.Alternatively, the recording material determination unit 30 and thecontrol unit 10 may be simply integrally formed, and configured to beadditionally attachable to the image forming apparatus 1.

Herein, an apparatus to which the recording material determination unit30 is attached is not limited to the image forming apparatus 1. Anyconveyance apparatus may be used as long as it has a configuration forconveying the recording material P and forming a loop on the recordingmaterial P. The present invention is applicable in a state in which therecording material determination unit 30 is attached to such anapparatus.

Furthermore, although an example of a laser beam printer has beendescribed in the above-described exemplary embodiments, the imageforming apparatus to which the present invention is applied is notlimited to the laser beam printer. The image forming apparatus may be aprinter with other printing methods such as an inkjet printer, or may bea copier.

Hereinafter, fourth to sixth exemplary embodiments of the presentinvention will be described with reference to the drawings. Thefollowing exemplary embodiments are only examples. The present inventionis not limited to the exemplary embodiments described herein. In thefollowing drawings, components that are not necessary for describing theexemplary embodiments will be omitted.

FIG. 14 is a configuration diagram of an image forming apparatusaccording to a fourth exemplary embodiment. The same components as thoseillustrated in FIG. 1 are assigned the same reference signs. Lastletters Y, M, C, and K of reference signs indicate that correspondingmembers are members for forming developer images of the respectivecolors of yellow (Y), magenta (M), cyan C, and black (K). When it is notnecessary to distinguish colors, the reference signs without the lastletters Y, M, C, and K are used herein. Photosensitive drums 11 serve asan image bearing member, and are driven to rotate during imageformation. Charging units (rollers) 12 charge the surfaces of therespective photosensitive drums 11 to a uniform potential. Exposureunits 13 scan and expose the surfaces of the respective photosensitivedrums 11 with light according to image data of images to be formed, tothereby form electrostatic latent images on the photosensitive drum 11.Development units 14 contain developers of the respective colors. Thedevelopment units 14 develop the electrostatic latent images on therespective photosensitive drums 11 by supplying the developers to theelectrostatic latent images on the photosensitive drums 11 using therespective developing rollers 15. Primary transfer rollers 16 output aprimary transfer bias, and transfer the developer images formed on thephotosensitive drums 11, onto the intermediate transfer belt 17, whichis an image bearing member and is stretched by rollers 180, 200 and 250.At this time, a color image is formed by transferring the developerimages on the respective photosensitive drums 11, onto the intermediatetransfer belt 17 in a superimposed manner.

The developer image formed on the intermediate transfer belt 17 isconveyed to a counter position of the secondary transfer roller 19 byrotation of the intermediate transfer belt 17. A sheet feeding roller 4feeds the recording material P stored in the cassette 2 to a conveyancepath. A conveyance roller 63 and a conveyance counter roller 60constitute a roller pair for conveying the recording material P. When aregistration sensor 340 detects the recording material P, the conveyanceroller 63 and the conveyance counter roller 60 temporarily stopconveying the recording material P. The conveyance roller 63 and theconveyance counter roller 60 restart conveying the recording material P,according to the timing at which the developer image formed on theintermediate transfer belt 17 comes to the counter position of thesecondary transfer roller 19. The secondary transfer roller 19 outputs asecondary transfer bias, thereby transferring the developer image on theintermediate transfer belt 17, onto the recording material P. Thesecondary transfer roller 19 is also involved in conveyance of therecording material P. That is, the secondary transfer roller 19 is amember that acts on the recording material P for transferring thedeveloper image onto the recording material P and is a member forconveying the recording material P. Then, at a fixing unit 210, heat andpressure are applied to the recording material P on which the developerimage has been transferred, whereby the developer image is fixed ontothe recording material P. The recording material P on which thedeveloper image has been fixed is output to a discharge tray 260 by adischarge roller 220.

In the present exemplary embodiment, grammage of the recording materialP is detected as a characteristic of the recording material P. Asillustrated in FIG. 14, a grammage detection sensor that detects thegrammage of the recording material P is provided on an upstream side ofthe secondary transfer roller 19 in a conveyance direction of therecording material P. The grammage detection sensor includes atransmission unit 310 and a reception unit 320. The transmission unit310 is arranged opposite the reception unit 320 across the conveyancepath. Furthermore, a guide roller 330 is arranged on the same side ofthe transmission unit 310. The guide roller 330 is a member forstabilizing conveyance position of the recording material P by absorbingvibration during conveyance of the recording material P. The guideroller 330 is an example of a contact member that contacts the recordingmaterial P. The transmission unit 310 and the guide roller 330 togetherwith the secondary transfer roller 19 are held by a secondary transferunit 230. The secondary transfer unit 230 is openable and closable inthe direction indicated by an arrow in FIG. 14, around a rotation shaft240 as a fulcrum. With this configuration, when the recording material Pbeing conveyed is jammed near the secondary transfer unit 230, the usercan easily remove the jammed recording material P. The grammage is amass of a recording material P per unit area, and the unit is [g/m²].

The transmission unit 310 and the reception unit 320 have a similarconfiguration. Each of the units 310 and 320 includes a piezoelectricelement, which is a mutual conversion element for mechanicaldisplacement and an electric signal, and an electrode terminal. In thetransmission unit 310, when a pulse voltage with a predeterminedfrequency is input to the electrode terminal, the piezoelectric elementoscillates to generate an ultrasonic wave, which is propagated in theair. When the ultrasonic wave reaches the recording material P, theultrasonic wave vibrates the recording material P. In this manner, theultrasonic wave generated by the transmission unit 310 is propagated tothe reception unit 320 through the recording material P. Thepiezoelectric element of the reception unit 320 generates on theelectrode terminal the output voltage according to the amplitude of thereceived ultrasonic wave. This is an operation principle of a case wherethe ultrasonic wave is transmitted and received using the piezoelectricelement.

Vibration of the conveyance roller 63 is transmitted to the recordingmaterial P being conveyed. This flapping caused by the vibration duringconveyance affects the detection result of grammage. The reason is asfollows. A tilt in the recording material P with respect to theultrasonic wave path changes the area of the recording material P thatis in contact with the ultrasonic wave, causing a fluctuation in theultrasonic wave to be propagated to the reception unit 320. The imageforming apparatus according to the present exemplary embodiment performsthe detection of grammage a plurality of times to suppress theabove-described influence. For increasing the number of detections ofgrammage, the image forming apparatus detects grammage even after therecording material P has reached the counter position of the secondarytransfer roller 19. Herein, if the rotation speed of the conveyanceroller 63 is higher than that of the secondary transfer roller 19, therecording material P is pulled in the conveyance direction to generate abending (loop) of the recording material P.

Reasons for occurrence of bending and for occurrence of an error in thedetection result of grammage due to the bending will be described withreference to FIGS. 15A to 15D and FIGS. 23A to 23C. In the case of FIG.15A, in which the recording material P is thin paper, even if bending ofthe recording material P occurs, the bending on the sensor can besuppressed by the guide roller 330. On the other hand, in the case ofFIG. 15B, in which the recording material P is thick paper, repulsion ofthe recording material P increases and the bending cannot be suppressedby the guide roller 330. This causes the bending that may lift up theguide roller 330. In this case, as illustrated in FIG. 15D, a tilt θoccurs in the recording material P between the transmission unit 310 andthe reception unit 320. Accordingly, the obtained grammage differs fromthat in the detection result of FIG. 15C, in which no tilt occurs in therecording material P. A rotation speed difference between the conveyanceroller 63 and the secondary transfer roller 19 is caused by the use ofdifferent driving sources. Nevertheless, even when the same drivingsource is used, the rotation speed difference may be caused by anotherfactor such as the difference in slippage between the roller and therecording material P. FIG. 23A illustrates the positional relationshipbetween the grammage detection sensor and the guide roller 330 viewed ina direction orthogonal to the surface of the recording material P. Asillustrated in FIGS. 15A to 15D, the transmission unit 310 of thegrammage detection sensor and the guide roller 330 are provided on thesame side with respect to the recording material P. On the opposite sideto the transmission unit 310 with respect to the recording material P,the reception unit 320 is provided, which is not illustrated in FIG.23A. FIGS. 23B and 23C are diagrams viewed in the conveyance directionof the recording material P. Herein, FIG. 23B illustrates the state inwhich no bending occurs in the recording material P. FIG. 23Cillustrates the state in which bending has occurred in the recordingmaterial P. The dotted line in FIG. 23C indicates the position of therecording material P when no bending occurs.

FIG. 16 is a functional block diagram illustrating a controlconfiguration of the image forming apparatus according to the presentexemplary embodiment. A main control unit 2000 controls the entire imageforming apparatus, and includes a timer 2010 and an image formationcontrol unit 3. How the timer 2010 is utilized will be described below.The image formation control unit 3 includes a grammage detection sensorcontrol unit 300 that controls the grammage detection sensor. Thegrammage detection sensor control unit 300 transmits an ultrasonic wavegeneration instruction to the transmission unit 310 and receives aresult from the reception unit 320. A type determination unit 2030determines grammage based on the detection result obtained by thegrammage detection sensor control unit 300. Furthermore, the typedetermination unit 2030 determines, based on the determined grammage,the type of recording material P and sets image forming conditions.Herein, the image forming conditions are conditions of which values arechanged depending on the type of recording material P. For example, theimage forming conditions include the conveyance speed of the recordingmaterial P, the voltage to be applied to the secondary transfer roller19, and a fixing temperature of the fixing unit 210. A bendingdetermination unit 2020 determines, based on the type of recordingmaterial P that has been determined by the type determination unit 2030,whether bending occurs, and notifies the grammage detection sensorcontrol unit 300 of the determination result. The grammage detectionsensor control unit 300 controls the timing for performing the grammagedetection, based on the determination result obtained by the bendingdetermination unit 2020.

FIG. 17 is a flowchart illustrating type determination processing of therecording material P. In step S101, the grammage detection sensorcontrol unit 300 measures the grammage of the recording material P usingthe grammage detection sensor. As illustrated in FIG. 15C, the processin step S101 is performed in a state in which the recording material Pis in a position where it is detectable by the grammage detectionsensor, but it has not reached the secondary transfer roller 19. In stepS102, the type determination unit 2030 determines the type of recordingmaterial P based on the measurement result obtained in step S101. Instep S103, the image formation control unit 3 determines whether thefront end of the recording material P has reached the secondary transferroller 19, and if not (No in step S103), the processing is repeated fromstep S101. The type determination unit 2030 can be configured todetermine the type of recording material based on a plurality ofmeasurement results of grammage, in repetition of steps S101 to S103.The bending determination unit 2020 determines, every time the typedetermination unit 2030 determines the type, whether the determined typeis the type that lifts up the guide roller 330, namely, the type thatgenerates bending, and notifies the grammage detection sensor controlunit 300 of the determination result. If the front end of the recordingmaterial P has reached the secondary transfer roller 19 (YES in stepS103), then in step S104, the grammage detection sensor control unit 300determines whether the determination result obtained by the bendingdetermination unit 2020 indicates that bending occurs. When therecording material is determined to be not the type that bends (NO instep S104), then in step S105, the grammage detection sensor controlunit 300 measures the grammage of the recording material P by thegrammage detection sensor. In step S106, the type determination unit2030 determines the type of recording material P. The type determinationunit 2030 may be configured to determine the type of recording materialP based on a plurality of previous measurement results of grammage. Instep S107, the grammage detection sensor control unit 300 determineswhether the rear end of the recording material P has passed through theconveyance roller 63, and if the rear end has not passed (NO in stepS107), the processing is repeated from step S104 until the rear endpasses through the roller 63. On the other hand, if it is determined instep S104 that the determination result obtained by the bendingdetermination unit 2020 indicates that the type of the recordingmaterial P is the type that generates bending (YES in step S104), thegrammage detection sensor control unit 300 discontinues grammagemeasurement by the grammage detection sensor after the front end of therecording material P has reached the secondary transfer roller 19. Theimage formation control unit 3 determines the time when the recordingmaterial P reaches the counter position of the secondary transfer roller19, based on the time measured by the timer 2010 in FIG. 16.

In this manner, whether bending occurs is determined based on the typeof recording material P that has been determined in a state in which therecording material P has not reached the counter position of thesecondary transfer roller 19. If it is determined that bending mayoccur, type determination for the recording material P is stopped afterthe recording material P has reached the counter position of thesecondary transfer roller 19. This can prevent erroneous detectioncaused by performing type determination in a state in which bending hasoccurred.

In the present exemplary embodiment, the type determination unit 2030determines, based on the grammage of the recording material P, the typeof recording material P. According to the determination result, thebending determination unit 2020 determines whether the recordingmaterial P lifts up the guide roller 330. Herein, information related tothe grammage of the recording material P includes information on thethickness of the recording material P. If the recording material P ismade of the same material, the larger the thickness of the recordingmaterial P, the larger the grammage of the recording material P. Theinformation on the thickness of the recording material P can beobtained, for example, by emitting light onto the recording material Pand receiving the transmitted light transmitted through the recordingmaterial P. In this case, for example, the transmission unit 310 and thereception unit 320 in FIG. 14 are respectively replaced with a lightemitting unit and a light receiving unit. At this time, the lightreceiving unit that receives transmitted light may be a photodiode, ormay be an area sensor or a line sensor that captures the received lightas an image. The line sensor is a sensor extending in a directionorthogonal to the conveyance direction of the recording material P, andcan capture an image while conveying the recording material P.

When the amount of light received by the light receiving unit is large,the type determination unit 2030 determines that the thickness of therecording material P is thin, and then determines that the type ofrecording material P is thin paper. When the amount of the receivedlight is small, the type determination unit 2030 determines that thethickness of the recording material P is thick, and then determines thatthe type of recording material P is thick paper. In this manner, byusing the thickness detection sensor that detects the thickness of therecording material P, the type of recording material P can be determinedsimilarly to the case where the grammage detection sensor according tothe present exemplary embodiment is used. Furthermore, if thick paperwith high stiffness lifts up the guide roller 330 and a tilt occurs inthe recording material P as illustrated in FIG. 15D, the amount of lighttransmitted through the recording material P changes. Therefore,obtained thickness information differs from the detection resultobtained in a state in which no tilt occurs in the recording material Pas in FIG. 15C.

In this manner, whether bending occurs is determined based on the typeof recording material P determined by the thickness detection sensor ina state in which the recording material P has not reached the counterposition of the secondary transfer roller 19, in a similar manner to thecase of using the grammage detection sensor. Subsequently, if it isdetermined that bending may occur, type determination for the recordingmaterial P using the thickness detection sensor may be stopped after therecording material P has reached the counter position of the secondarytransfer roller 19.

Next, a fifth exemplary embodiment will be described mainly on adifference from the fourth exemplary embodiment. FIG. 18 is aconfiguration diagram of an image forming apparatus according to thepresent exemplary embodiment. The image forming apparatus according tothe present exemplary embodiment differs from the image formingapparatus according to the fourth exemplary embodiment in that a surfaceproperty detection sensor is added. The surface property detectionsensor for detecting the surface information of the recording materialP, as one characteristic of the recording material P, includes a lightemitting element 350 and a light receiving element 360 (photodiode) as alight receiving unit that receives light. The guide roller 330 isarranged at a position facing the surface property detection sensor. Thetransmission unit 310 and the guide roller 330 together with thesecondary transfer roller 19 are held by the secondary transfer unit230. In the present exemplary embodiment, the light receiving element360 receives the light emitted from the light emitting element 350 andreflected on the recording material P as reflected light. As illustratedin FIG. 18, the light receiving element 360 and the light emittingelement 350 are provided on the same side with respect to the recordingmaterial P. FIGS. 24A to 24C illustrate the positional relationshipbetween the grammage detection sensor, the surface property detectionsensor, the guide roller 330, and the recording material P. Asillustrated in FIG. 24A, the transmission unit 310 of the grammagedetection sensor and the guide roller 330 are provided on the same sidewith respect to the recording material P. On the opposite side to thetransmission unit 310 and the guide roller 330 with respect to therecording material P, there are provided the reception unit 320 of thegrammage detection sensor and the light emitting element 350 and thelight receiving element 360 of the surface property detection sensor,although they are not illustrated in FIG. 24A. FIGS. 24B and 24C arediagrams viewed in the conveyance direction of the recording material P.Herein, FIG. 24B illustrates a state in which no bending occurs in therecording material P. FIG. 24C illustrates a state in which bending hasoccurred in the recording material P. In FIGS. 24B and 24C, the dottedarrows indicate light emitted from the light emitting element 350,reflected on the recording material P, and then received by the lightreceiving element 360. The dotted line in FIG. 24C indicates theposition of the recording material P when no bending occurs. The lightreceiving unit may be an area sensor or a line sensor that captures thereceived light as an image.

FIG. 19 is a functional block diagram illustrating a controlconfiguration of the image forming apparatus according to the presentexemplary embodiment. A surface property detection sensor control unit370 controls light emission of the light emitting element 350 andobtains the amount of light received by the light receiving element 360.In the present exemplary embodiment, the type determination unit 2030determines the type of recording material P based on the detectionresult obtained by the grammage detection sensor control unit 300 or thesurface property detection sensor control unit 370, and controls imageforming conditions. In the present exemplary embodiment, the type ofrecording material P is determined based on the grammage until the frontend of the recording material P reaches the counter position of thesecondary transfer roller 19. On the other hand, after the front end ofthe recording material P has reached the counter position of thesecondary transfer roller 19, the type of recording material P isdetermined based on the surface property if the recording material P isthe one that does not bend.

FIG. 20 is a flowchart illustrating type determination processing of therecording material P. Processing in steps S201 to S204 and theprocessing in S207 are the same as the processing in steps S101 to S104and the processing in step S107 in FIG. 17. In the present exemplaryembodiment, after the front end of the recording material P has reachedthe counter position of the secondary transfer roller 19, if therecording material P is not the one that may bend, the type of recordingmaterial P is determined based on the surface property. Specifically, instep S205, the surface property detection sensor control unit 370measures the surface proper of the recording material P by the surfaceproperty detection sensor. In step S206, the type determination unit2030 determines the type of recording material P based on the surfaceproperty of the recording material P.

In the present exemplary embodiment, type determination in step S202 isperformed based on the grammage. The type determination, however, may beperformed based on the grammage in combination with the surfaceproperty. Furthermore, in the present exemplary embodiment, the typedetermination in step S206 is performed based on the surface property.The type determination, however, may be performed based on the surfaceproperty in combination with the grammage, or only based on thegrammage.

Furthermore, as described in the fourth exemplary embodiment, a sensorthat detects the thickness may be used instead of a sensor that detectsgrammage. That is, while the type determination in step S202 isperformed based on the grammage in the present exemplary embodiment, thetype determination may be performed based on the thickness.Alternatively, the type determination may be performed based on thethickness in combination with the surface property. Furthermore, in thepresent exemplary embodiment, the type determination in step S206 isperformed based on the surface property. The type determination,however, may be performed based on the thickness in combination with thesurface property, or only based on the thickness.

Next, a sixth exemplary embodiment will be described mainly on adifference from the fifth exemplary embodiment. In the present exemplaryembodiment, the occurrence of bending is determined by comparing thedetection results obtained by the surface property detection sensorbetween before and after the front end of the recording material P hasreached the counter position of the secondary transfer roller 19.

FIG. 21 is a functional block diagram illustrating a controlconfiguration of an image forming apparatus according to the presentexemplary embodiment. As described above, the bending determination unit2020 determines the occurrence of bending based on the detection resultsobtained by the surface property detection sensor before and after thefront end of the recording material P has reached the counter positionof the secondary transfer roller 19, and notifies the grammage detectionsensor control unit 300 of the determination result. Specifically, whenbending occurs, the amount of light received by the light receivingelement 360 of the surface property detection sensor decreases ascompared with that in the case where no bending occurs. Accordingly, thebending determination unit 2020 determines that bending has occurred,when the amount of light received by the light receiving element 360after the front end of the recording material P has reached the counterposition of the secondary transfer roller 19 decreases by apredetermined threshold or more from that obtained before the front endreaches the counter position.

FIG. 22 is a flowchart illustrating type determination processing of therecording material P. In step S301, the surface property detectionsensor control unit 370 measures the surface property of the recordingmaterial P by the surface property detection sensor. The amount of lightreceived by the light receiving element 360 at this time is defined asa1. In step S302, the grammage detection sensor control unit 300measures the grammage of the recording material P by the grammagedetection sensor. In step S303, the type determination unit 2030determines the type of recording material P based on the grammage. Instep S304, it is determined whether the front end of the recordingmaterial P has reached the secondary transfer roller 19. If it isdetermined that the front end has reached the secondary transfer roller19 (YES in step S304), in step S305, the surface property detectionsensor control unit 370 measures the surface property of the recordingmaterial P by the surface property detection sensor. The amount of lightreceived by the light receiving element 360 at this time is defined asa2. In step S306, the bending determination unit 2020 determines whethera value obtained by subtracting a2 from a1 is larger than apredetermined threshold. If the obtained value is larger than thepredetermined threshold (YES in step S306), the bending determinationunit 2020 determines that bending has occurred. When the bending doesnot occur (NO in step S306), then in step S307, the grammage detectionsensor control unit 300 measures the grammage. Then in step S308, thetype determination unit 2030 determines the type of recording material Pbased on the grammage. On the other hand, when the bending has occurred(YES in step S306), then in step S309, the type determination unit 2030performs control for removing the bending of the recording material P bydecreasing the rotation speed of the conveyance roller 63. In step S310,the image formation control unit 3 determines whether the rear end ofthe recording material P has passed through the conveyance roller 63,and if not (NO in step S301), the processing is repeated from step S305until the rear end of the recording material P passes through the roller63.

In the present exemplary embodiment, the rotation speed of theconveyance roller 63 is controlled in step S309 for removing thebending. Alternatively, the rotation speed of the secondary transferroller 19 may be controlled. Occurrence of bending decreases theintensity (amplitude) of the ultrasonic wave received by the grammagedetection sensor. Accordingly, occurrence of the bending may bedetermined based on the detection results obtained by the grammagedetection sensor, instead of the surface property detection sensor,before and after the recording material P has reached the counterposition of the secondary transfer roller 19. Furthermore, occurrence ofbending decreases the amount of light received by the thicknessdetection sensor. Accordingly, occurrence of bending may be determinedbased on the detection results obtained by the thickness detectionsensor, instead of the surface property detection sensor, before andafter the recording material P has reached the counter position of thesecondary transfer roller 19. Furthermore, in the present exemplaryembodiment, the sensor used for determining occurrence of bending andthe sensor used for determining the type of recording material areseparately provided. However, the same sensor may be used for thesepurposes.

In this manner, in the present exemplary embodiment, occurrence ofbending is detected by comparing the detection results obtained by thesensor before and after the recording material P has reached the counterposition of the secondary transfer roller 19. When bending is detected,detection of the recording material type is not performed after therecording material P has reached the counter position of the secondarytransfer roller 19. This configuration enables improvement in thedetection accuracy of the recording material type. Furthermore, whenbending is detected, it is possible to control a conveyance member ofthe recording material P to remove the bending.

The above-described exemplary embodiments have mainly described the casewhere the number of the target recording material P is one. Whensuccessively performing printing on a plurality of recording materialsP, the succeeding recording materials P are likely to have the same typeas the first recording material P. Thus, the type determinationprocessing may not be performed on the succeeding recording materials P.

Alternatively, control may be performed such that the measurement of thesucceeding (second and subsequent) recording materials P can be switchedbased on the measurement result of the first recording material P. Thatis, whether bending occurs is determined based on the type of recordingmaterial P that has been determined in a state in which the firstrecording material P has not reached the counter position of thesecondary transfer roller 19. If it is determined that bending may occurin the first recording material P, type determination for the recordingmaterial P is stopped after the second and subsequent recordingmaterials P following the first recording material P have reached thecounter position of the secondary transfer roller 19. On the other hand,if it is determined that bending does not occur in the first recordingmaterial P, type determination for the recording material P is performedafter the second and subsequent recording materials P following thefirst recording material P have reached the counter position of thesecondary transfer roller 19.

The exemplary embodiments of the present invention can also beimplemented by processing of supplying a program for implementing one ormore functions of the above-described exemplary embodiments to a systemor an apparatus via a network or a storage medium, and one or moreprocessors in a computer of the system or the apparatus reading andexecuting the program. The exemplary embodiments of the presentinvention can also be implemented by a circuit (for example,application-specific integrated circuit (ASIC)) that implements one ormore functions.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Applications No.2014-233131, filed Nov. 17, 2014, and No. 2014-242303, filed Nov. 28,2014, which are hereby incorporated by reference herein in theirentirety.

What is claimed is:
 1. An image forming apparatus comprising: an imageforming unit configured to form an image on a recording material; afirst detection unit including a transmission unit configured totransmit an ultrasonic wave and a reception unit configured to receivethe transmitted ultrasonic wave; a first conveyance unit arranged on anupstream side of the first detection unit in a conveyance direction ofthe recording material, and configured to convey the recording materialtoward a position between the transmission unit and the reception unit;a second conveyance unit arranged on a downstream side of the firstdetection unit in the conveyance direction, and configured to convey therecording material conveyed by the first conveyance unit, wherein thefirst conveyance unit and the second conveyance unit form a loop on therecording material by conveying the recording material at differentspeeds; and a control unit configured to control an image formingcondition for forming an image on the recording material by the imageforming unit, based on the ultrasonic wave received via the recordingmaterial in a period in which no loop is formed on the recordingmaterial by the first conveyance unit and the second conveyance unit. 2.The image forming apparatus according to claim 1, wherein the period inwhich no loop is formed on the recording material is a period in whichthe recording material is conveyed by either one of the first conveyanceunit and the second conveyance unit, and the recording material is notconveyed by the other one.
 3. The image forming apparatus according toclaim 2, wherein the period in which no loop is formed on the recordingmaterial is a period from a time point at which a front end of therecording material passes through the position between the transmissionunit and the reception unit to a time point at which the front end ofthe recording material reaches the second conveyance unit.
 4. The imageforming apparatus according to claim 2, wherein the period in which noloop is formed on the recording material is a period from a time pointat which a rear end of the recording material passes through the firstconveyance unit to a time point at which the rear end of the recordingmaterial passes through the position between the transmission unit andthe reception unit.
 5. The image forming apparatus according to claim 1,wherein a period in which a loop is formed on the recording material bythe first conveyance unit and the second conveyance unit is a period inwhich the recording material is conveyed by both of the first conveyanceunit and the second conveyance unit.
 6. The image forming apparatusaccording to claim 5, wherein the period in which a loop is formed onthe recording material is a period from a time point at which a frontend of the recording material reaches the second conveyance unit to atime point at which a rear end of the recording material passes throughthe first conveyance unit.
 7. The image forming apparatus according toclaim 5, wherein the ultrasonic wave is not transmitted in the period inwhich a loop is formed on the recording material.
 8. The image formingapparatus according to claim 1, wherein the transmission unit and thereception unit are arranged facing each other, and the reception unitreceives the ultrasonic wave transmitted through the recording material.9. The image forming apparatus according to claim 1, wherein the controlunit controls the image forming condition based on a detection result ofthe recording material that has been obtained by the first detectionunit in a period in which a speed of the recording material is constant.10. The image forming apparatus according to claim 1, wherein thecontrol unit controls the image forming condition based on a detectionresult of the recording material that has been obtained by the firstdetection unit in a period in which a speed of the recording material isincreased or decreased.
 11. The image forming apparatus according toclaim 1, further comprising a second detection unit including anirradiation unit configured to emit light and a light receiving unitconfigured to receive the emitted light, wherein the control unitcontrols the image forming condition based on the light received via therecording material.
 12. The image forming apparatus according to claim11, wherein the light receiving unit receives light emitted by theirradiation unit and reflected on the recording material.
 13. The imageforming apparatus according to claim 11, wherein the light receivingunit is an image capturing unit configured to capture received light asan image.
 14. The image forming apparatus according to claim 11, whereinthe control unit controls the image forming condition based on adetection result of the recording material that has been obtained by thesecond detection unit in a period in which a speed of the recordingmaterial is constant.
 15. The image forming apparatus according to claim11, wherein the control unit controls the image forming conditionwithout using a detection result of the recording material that has beenobtained by the second detection unit in a period in which a speed ofthe recording material is increased or decreased.
 16. The image formingapparatus according to claim 11, wherein light is not emitted by theirradiation unit in a period in which a speed of the recording materialis increased or decreased.
 17. The image forming apparatus according toclaim 11, wherein the first detection unit and the second detection unitare arranged in a direction orthogonal to the conveyance direction. 18.The image forming apparatus according to claim 11, further comprising acontact member configured to contact the recording material irradiatedwith light, on a second surface of the recording material that isopposite to a first surface irradiated with light, wherein light isemitted by the irradiation unit onto a predetermined region of the firstsurface, and the contact member contacts the recording material in apredetermined region of the second surface that is opposite to thepredetermined region of the first surface.
 19. The image formingapparatus according to claim 1, wherein the second conveyance unit is atransfer unit configured to transfer an image onto the recordingmaterial conveyed by the first conveyance unit.
 20. The image formingapparatus according to claim 1, wherein the image forming unit includesa fixing unit configured to fix an image onto the recording material,and wherein the image forming condition is a temperature at which thefixing unit fixes the image onto the recording material.
 21. The imageforming apparatus according to claim 1, wherein the image forming unitincludes a transfer unit configured to transfer an image onto therecording material, and wherein the image forming condition is a valueof a voltage to be applied to the transfer unit.
 22. The image formingapparatus according to claim 1, wherein the image forming condition is aconveyance speed of the recording material.
 23. A recording materialdetermination unit used in a conveyance apparatus including a firstconveyance unit configured to convey a recording material, and a secondconveyance unit arranged on a downstream side of the first conveyanceunit in a conveyance direction of the recording material, and configuredto convey the recording material conveyed by the first conveyance unit,the first conveyance unit and the second conveyance unit forming a loopon the recording material by conveying the recording material atdifferent speeds, the recording material determination unit comprising:a first detection unit including a transmission unit configured totransmit an ultrasonic wave, and a reception unit configured to receivethe transmitted ultrasonic wave; and a determination unit configured todetermine grammage of the recording material in a state in which therecording material determination unit is attached to the conveyanceapparatus so that the first detection unit is positioned between thefirst conveyance unit and the second conveyance unit, based on theultrasonic wave received via the recording material in a period in whichno loop is formed on the recording material by the first conveyance unitand the second conveyance unit.
 24. An image forming apparatuscomprising: an image forming unit configured to form an image on arecording material; a detection unit configured to detect acharacteristic of the recording material; a control unit configured tocontrol an image forming condition for forming an image on the recordingmaterial by the image forming unit, based on the detected characteristicof the recording material; a first conveyance unit arranged on anupstream side of the detection unit in a conveyance direction of therecording material, and configured to convey the recording materialtoward the detection unit; and a second conveyance unit arranged on adownstream side of the detection unit in the conveyance direction, andconfigured to convey the recording material conveyed by the firstconveyance unit, wherein the control unit determines, based on adetection result of a characteristic of the recording material that hasbeen obtained at a first timing that is before a front end of therecording material reaches the second conveyance unit, whether thedetection unit is to detect a characteristic of the recording materialat a second timing that is after the front end of the recording materialreaches the second conveyance unit.
 25. An image forming apparatuscomprising: an image forming unit configured to form an image on arecording material; a detection unit configured to detect acharacteristic of the recording material; a control unit configured tocontrol an image forming condition for forming an image on the recordingmaterial by the image forming unit, based on the detected characteristicof the recording material; a first conveyance unit arranged on anupstream side of the detection unit in a conveyance direction of therecording material, and configured to convey the recording materialtoward the detection unit; and a second conveyance unit arranged on adownstream side of the detection unit in the conveyance direction, andconfigured to convey the recording material conveyed by the firstconveyance unit, wherein the control unit determines, based on adetection result of a characteristic of a preceding first recordingmaterial that has been obtained at a first timing that is before a frontend of the first recording material reaches the second conveyance unit,whether the detection unit is to detect a characteristic of a succeedingsecond recording material at a second timing that is after a front endof the second recording material reaches the second conveyance unit. 26.The image forming apparatus according to claim 24, wherein the detectionunit includes a transmission unit configured to transmit an ultrasonicwave to the recording material, and a reception unit configured toreceive the ultrasonic wave transmitted through the recording material,and wherein the detection unit detects grammage of the recordingmaterial based on the received ultrasonic wave.
 27. The image formingapparatus according to claim 24, wherein the detection unit includes anirradiation unit configured to emit light onto the recording material,and a light receiving unit configured to receive the light emitted fromthe irradiation unit and transmitted through the recording material, andwherein the detection unit detects a thickness of the recording materialbased on the received light.
 28. The image forming apparatus accordingto claim 24, further comprising a contact member configured to contactthe recording material, wherein the first conveyance unit and the secondconveyance unit form a loop on the recording material by conveying therecording material at different speeds, wherein the control unitdetermines whether a loop on the recording material is suppressible bythe contact member, based on the detection result of the characteristicof the recording material that has been obtained at the first timing,and wherein in a case where the loop on the recording material issuppressible, the detection unit detects a characteristic of therecording material at the second timing, and in a case where the loop onthe recording material is not suppressible, the detection unit does notdetect a characteristic of the recording material at the second timing.29. The image forming apparatus according to claim 24, wherein thesecond conveyance unit is a transfer unit configured to transfer animage onto the recording material conveyed by the first conveyance unit.30. The image forming apparatus according to claim 24, wherein the imageforming unit includes a fixing unit configured to fix an image onto therecording material, and wherein the image forming condition is atemperature at which the fixing unit fixes the image onto the recordingmaterial.
 31. The image forming apparatus according to claim 24, whereinthe image forming unit includes a transfer unit configured to transferan image onto the recording material, and wherein the image formingcondition is a value of a voltage to be applied to the transfer unit.32. The image forming apparatus according to claim 24, wherein the imageforming condition is a conveyance speed of the recording material. 33.An image forming apparatus comprising: an image forming unit configuredto form an image on a recording material; a first detection unit and asecond detection unit each configured to detect a characteristic of therecording material; a control unit configured to control an imageforming condition for forming an image on the recording material by theimage forming unit, based on the characteristic of the recordingmaterial that has been detected by at least either one of the firstdetection unit and the second detection unit; a first conveyance unitarranged on an upstream side of the first detection unit and the seconddetection unit in a conveyance direction of the recording material, andconfigured to convey the recording material toward the first detectionunit and the second detection unit; and a second conveyance unitarranged on a downstream side of the first detection unit and the seconddetection unit in the conveyance direction, and configured to convey therecording material conveyed by the first conveyance unit, wherein thecontrol unit determines, based on a detection result of thecharacteristic of the recording material that has been obtained at afirst timing that is before a front end of the recording materialreaches the second conveyance unit, whether the second detection unit isto detect a characteristic of the recording material at a second timingthat is after the front end of the recording material reaches the secondconveyance unit.
 34. An image forming apparatus comprising: an imageforming unit configured to form an image on a recording material; afirst detection unit and a second detection unit each configured todetect a characteristic of the recording material; a control unitconfigured to control an image forming condition for forming an image onthe recording material by the image forming unit, based on thecharacteristic of the recording material that has been detected by atleast either one of the first detection unit and the second detectionunit; a first conveyance unit arranged on an upstream side of the firstdetection unit and the second detection unit in a conveyance directionof the recording material, and configured to convey the recordingmaterial toward the first detection unit and the second detection unit;and a second conveyance unit arranged on a downstream side of the firstdetection unit and the second detection unit in the conveyancedirection, and configured to convey the recording material conveyed bythe first conveyance unit, wherein the control unit determines, based ona detection result of a characteristic of a preceding first recordingmaterial that has been obtained at a first timing that is before a frontend of the first recording material reaches the second conveyance unit,whether the second detection unit is to detect a characteristic of asucceeding second recording material at a second timing that is after afront end of the second recording material reaches the second conveyanceunit.
 35. The image forming apparatus according to claim 33, wherein thefirst detection unit or the second detection unit includes atransmission unit configured to transmit an ultrasonic wave to therecording material, and a reception unit configured to receive theultrasonic wave transmitted through the recording material, and whereinthe first detection unit or the second detection unit detects grammageof the recording material based on the received ultrasonic wave.
 36. Theimage forming apparatus according to claim 33, wherein the firstdetection unit or the second detection unit includes an irradiation unitconfigured to emit light onto the recording material, and a lightreceiving unit configured to receive the emitted light transmittedthrough the recording material, and wherein the first detection unit orthe second detection unit detects a thickness of the recording materialbased on the received light.
 37. The image forming apparatus accordingto claim 33, further comprising a contact member configured to contactthe recording material, wherein the first conveyance unit and the secondconveyance unit form a loop on the recording material by conveying therecording material at different speeds, wherein the control unitdetermines whether a loop on the recording material is suppressible bythe contact member, based on the detection result of the characteristicof the recording material that has been obtained at the first timing,and wherein in a case where the loop on the recording material issuppressible, the second detection unit detects a characteristic of therecording material at the second timing, and in a case where the loop onthe recording material is not suppressible, the second detection unitdoes not detect a characteristic of the recording material at the secondtiming.
 38. The image forming apparatus according to claim 33, whereinthe first detection unit includes an irradiation unit configured to emitlight onto the recording material, and a light receiving unit configuredto receive the emitted light reflected on the recording material ortransmitted through the recording material, and wherein in a case wherea difference between an amount of light received at the first timing andan amount of light received at the second timing is larger than athreshold, the control unit determines that the second detection unit isnot to detect a characteristic of the recording material at the secondtiming.
 39. The image forming apparatus according to claim 33, whereinthe first detection unit includes a transmission unit configured totransmit an ultrasonic wave to the recording material, and a receptionunit configured to receive the ultrasonic wave transmitted through therecording material, and wherein in a case where a difference between anintensity of the received ultrasonic wave at the first timing and anintensity of the received ultrasonic wave at the second timing is largerthan a threshold, the control unit determines that the second detectionunit is not to detect a characteristic of the recording material at thesecond timing.
 40. The image forming apparatus according to claim 33,wherein the second conveyance unit is a transfer unit configured totransfer an image onto the recording material conveyed by the firstconveyance unit.
 41. The image forming apparatus according to claim 33,wherein the image forming unit includes a fixing unit configured to fixan image onto the recording material, and wherein the image formingcondition is a temperature at which the fixing unit fixes the image ontothe recording material.
 42. The image forming apparatus according toclaim 33, wherein the image forming unit includes a transfer unitconfigured to transfer an image onto the recording material, and whereinthe image forming condition is a value of a voltage to be applied to thetransfer unit.
 43. The image forming apparatus according to claim 33,wherein the image forming condition is a conveyance speed of therecording material.